A fuel cell directly converts the chemical energy of fuel into electrical energy with a high conversion efficiency, and produces noise and vibrations to only a small extent. Therefore, the fuel cell is expected to be a power supply in various fields such as portable instruments, automobiles, trains, and cogeneration.
A polymer electrolyte fuel cell includes a stack formed by stacking several tens to several hundreds of cells, each of the cells having a structure in which an anode and a cathode that support a catalyst (e.g., platinum) are disposed on either side of an ion-conductive polymer membrane (ion-exchange membrane), and plate-like separators are disposed on the outer side of the anode and the outer side of the cathode. The polymer electrolyte fuel cell may utilize a ribbed electrode configuration in which grooves that serve as flow passages for a fuel gas (e.g., hydrogen) and an oxidant gas (e.g., air) are formed in the surface of each electrode that faces the separator, or a ribbed separator configuration in which such grooves are formed in the surface of each separator (see Patent Document 1, for example).
The plate-like separator is required to exhibit high gas impermeability in order to completely separately supply the fuel gas and the oxidant gas to the electrodes. The plate-like separator is also required to exhibit high conductivity in order to reduce the internal resistance of the cell and increase the electricity generation efficiency. Since the stack must be strongly fastened during assembly so that the single cells adhere closely, high strength is desired for the separator material. When a fuel cell is provided in an automobile, cracking or breakage may occur due to vibrations, impact, expansion/contraction caused by a change in temperature, or the like. Therefore, the separator material is required to exhibit properties that suppress such cracking or breakage.
A carbonaceous material has been used for the separator for which the above properties are required. A carbon/cured resin formed body produced by integrally binding a carbon powder (e.g., graphite) using a thermosetting resin as a binder has been suitably used as the separator material.
A fuel cell separator has a drawback in which the groove (gas passage) may be clogged by water produced during electricity generation. In order to eliminate the above drawback, short fibers that exhibit water repellency may be provided on the surface of the groove (gas passage) (see Patent Document 2, for example), or the surface of the groove (gas passage) may be hydrophilized, for example. However, a post-treatment may be required when using the hydrophilization treatment, or the cell performance may deteriorate due to an increase in contact resistance of the separator when using the above method.